1. Field of the Invention
The present invention relates to of a rice plant as a new variety which is obtained by crossing the rice plant varieties “Koshihikari” with “Kasalath” and has improvements in both lodging resistance and grain size, and a method for producing it.
2. Related Art
Koshihikari is a representative rice plant variety of the Japonica type rice developed in Japan which has been supported by many consumers as a good taste variety over a half century. Koshihikari, of which the cropping acreage has been increased along with the improvement of cultivation techniques and the intention for better taste of consumers every year, is the variety cultivated most abundantly in Japan. Also, Koshihikari has been progressively cultivated in more northern regions, and thus the area of its cultivation can be expected to be further increased in future.
On the other hand, since Koshihikari is a long culmed variety, it is susceptible to lodging by storm such as typhoon and the early maturing variety is apt to have smaller grains. Therefore, there is a need for an improved variety of Koshihikari which maintains good taste as the characteristic of Koshihikari and has an excellent lodging resistance.
It has hitherto been tried to produce short-culmed varieties, i.e. to dwarf the culm, of rice plants including Koshihikari. As a technique for such attempts, back cross or backcrossing has been conventionally used in which one of parents is crossed again with the F1 hybrid (first filial generation). Particularly, according to continuous backcross in which backcross is carried out continuously, it is possible to produce a congenic line by incorporating a specific gene (a parent carrying the gene being referred to as donor parent), into the genetic background of one of the parents (recurrent parent).
However, the backcross technique is based on the conventional breeding techniques and thus requires a lot of time and labor for substituting genes on a chromosome. Furthermore, it is necessary in the course of backcross to conduct selections repeatedly on the basis of phenotypes, while a lot of experience is required for the selection and it may also be that the results of selection wilt depend on persons who conduct selections. On the other hand, it may be also contemplated to take out a specific gene and to introduce it into a target variety on the basis of the technology of genetic engineering, but the other means which is not based on the technologies of genetic engineering and particularly genetic recombination technique should be examined in consideration of the recent trend of consumers for avoiding genetically modified organisms (GMO).
Thus, efficient methods which can shorten breeding time and be of high reproducibility in relation to the production techniques have been searched with using the conventional breeding techniques without depending on genetic recombination technology. Such an enhancement of the efficiency is also believed to be useful for avoiding the contamination or remaining of the genes other than from the donor parent of the target gene in the other regions on the chromosome. Thus, the so-called marker breeding technique has been paid attention as a method for solving such problems. The marker breeding technique is a technique, which is primarily based on the conventional breeding technique, while the selection is carried out on the basis of the genetic information and technology such as DNA marker in its selection process. Particularly, the decoding of the genome of rice has already been accomplished in relation to rice plant, and investigations are now advanced for utilizing the techniques of genome analysis for the breeding or discrimination of varieties.
For example, multiple genes involved in the heading time have been reported as the result of analysis of gene loci relating to quantitative trait locus (QTL), and it has further been reported that a variety of rice plants exhibiting different heading times could have been developed with DNA markers obtained from such genes (Plant Physiol., 127, 1425-, 200 1). The DNA markers of which breeding methods have been examined include, for example, RFLP (Restriction Fragment Length Polymorphism), RAPD (Random Amplified Polymorphic DNA), AFLP (Amplified Fragment Length Polymorphism), SSR (Simple Sequence Repeat), CAPS (Cleaved Amplified Polymorphic Sequences), and the like.
As regards the technique discriminating the rice variety inclusive of Koshihikari, Japanese Patent Laid-Open Publication No, 2004-65251 discloses a microsatellite marker and a method for distinguishing varieties with it.
Also, International Publication WO 2004/066719 discloses that the lodging resistance of a rice plant has been improved with a marker obtained by the research of single nucleotide polymorphisms (SNPs). However, the variety used as the donor parent in this publication, which exhibits semi-dwarfness, does not affect yield trait, and decorticated grain size was not improved in the improved varieties obtained in practice. That is, in the improved variety described in the publication, while the yield appeared to have been increased in the practical breeding due to the culm shortening and increased heads, the decorticated grain had the size similar to that of Koshihikari or the like and thus the grain size or the improved variety was not increased (please see the column (v) on page 25 and Table 8 of this publication).
Generally, the terms “dwarfness” or “semi-dwarfness” as used in the improved variety mean that the culm length is shortened than normal types and the ear length and particle size of seeds are dwarfed, or that the culm length is shortened without affecting the yield trait including the ear length and the particle size of seeds. The increase of the yield is often observed as the result of stable growing of rice by the improvement of the rice variety to shorten the culm length and avoid lodging, but such dwarfness does not always ensure the increase of the grain size. While larger grain size can be said certainly advantageous. In view of processes including the cooking of rice or the other materials, it can be also said improved marketability for rice which is the staple food in many Asian countries including Japan to have good taste and large grain size.
Thus, a further improved variety of rice other than genetically modified organisms which maintains the good taste of Koshihikari and has an excellent lodging resistance as well as a large grain size is still desired.